Tuning of musical instruments

ABSTRACT

Apparatus (1) for varying the pitch of the strings (12) of a guitar (15) comprises a respective adjusting mechanism (10) for each string. This mechanism includes an externally threaded tubular member (20) within which one end of the string (12) is secured. Tension is applied to the string by a coil spring (124) which has one end fixed to the tubular member (20). A drive motor (34) is arranged to rotate a gear (26) whereby longitudinal movement of the tubular member (20) is effected to vary the tension in the string (12). The rotation of the drive motor (34) is effected by an electronic circuit arranged to tune the pitch of the string a reference.

The present invention relates to apparatus for varying the pitch of astretched string and to a musical instrument incorporating suchapparatus.

It is known to provide tuning apparatus comprising a sensor for sensingthe pitch of a vibrating stretched string, and an indicator forindicating whether the sensed pitch corresponds to a predeterminedreference pitch. Where there is no correspondence, the tension of thestring is adjusted manually until the indicator shows such acorrespondence.

One object of the present invention is to provide apparatus for varyingthe pitch of a stretched string automatically.

According to a first aspect of the present invention, there is providedapparatus for automatically varying the pitch of stretched string, saidapparatus comprising detecting means arranged to produce a signalrepresentative of the pitch produced by vibration of the stretchedstring, comparing means arranged to compare said representative signalwith a predetermined reference and to produce an output dependent uponsaid comparison, and adjusting means arranged in response to said outputto adjust said stretched string such that its pitch is varied.

The adjusting means may be arranged to vary the tension and/or thelength of the stretched airing such that its pitch is varied.

Apparatus of the invention enables the pitch of the string to beprecisely adjusted, or tuned, to the predetermined reference.

In an embodiment, said adjusting means comprises resilient means coupledto one end of the string to tension the string, said resilient meansbeing maintained under strain opposing the tension of said stretchedstring, and means for adjusting the tension of said stretched string.

For example, said tension adjusting means may comprise drive meanscoupled to one end of the stretched string, and being actuable to adjustthe tension applied in response to said output.

Said adjusting means may also comprise drive means arranged to apply astrain to one end of the string, and being actuable to adjust the strainapplied in response to said output.

In an embodiment, said adjusting means comprises a member attachable tosaid end of the string and coupled to said drive means, for example, byway of gear means. Advantageously, the member carries a screw-threadarranged to co-operate with said gear means.

In an embodiment, said gear means comprises a gear, arranged to berotated by said drive means, and co-operating with the screw-thread ofsaid member whereby rotation of said gear causes movement of said memberlongitudinally of a string at%ached thereto. Said member attachable tothe string may comprise a tubular member within which the stringextends. The screw-thread may be provided externally of said tubularmember and arranged for engagement with said gear means. Alternatively,the drive means may be directly coupled to said tubular member.

Preferably, said adjusting means has a null position in which saidmember is located intermediate extreme positions to which the member ismovable longitudinally. This is advantageous when attaching a new stringto the apparatus as it enables the member to be moved away from the nullposition in either direction. Preferably, null position switch means areprovided and are arranged to signal when said adjusting means is in itsnull position.

The invention also extends to adjusting means for varying the strain ofan elongate member, said adjusting means comprising resilient meanscoupled to one end of said member and arranged to apply strain thereto,said resilient means also being maintained under strain which opposesthe strain of said elongate member, and further comprising separatemeans for adjusting the strain of said elongate member.

According to a further aspect of the invention, there is providedapparatus for varying the pitch of a stretched string comprising meansmaintaining a strain on said string, and separate means for adjustingthe tension of said string to vary its pitch, wherein said adjustingmeans is arranged to vary the tension in said string in opposition tosaid maintaining means.

In an embodiment, the apparatus comprises storage means for storing saidpredetermined reference. Preferably, the storage means is arranged tostore a plurality of reference values, and selector means are providedfor selecting one of the stored values for use as the reference by saidcomparing means.

Interface means may be provided and arranged to enable the input and/orvariation of the values stored in the storage means.

Indicator means arranged to be responsive to the output of saidcomparing means may be provided. Advantageously, the indicator meanscomprises visual display means. Said display means may be arranged toindicate whether the pitch of the stretched string is below, above orsubstantially equal to said reference. In an embodiment, the indicatormeans is arranged to indicate the output of the comparing means duringadjustment of the string.

The detecting means arranged to produce a signal representative of pitchmay be a vibration sensor arranged proximate to, or in contact with,said string. In an embodiment said detecting means comprisespiezoelectric means.

In a preferred embodiment, the apparatus is arranged for automaticallyvarying the pitch of a plurality of strings. Control means may beprovided for actuating the apparatus to vary the pitch of one or morestrings, the control means comprising selector means for selecting thestring or strings whose pitch is to be varied. The selector meanscomprises individual string selection means arranged to selectindividual ones of the plurality of strings. Additionally and/oralternatively, the selector means comprises master selection meansarranged to enable selection of all of the strings.

In a preferred embodiment, said control means comprises processor meansarranged to actuate said adjusting means, said processor means beingarranged to receive select signals from said selector means and todetermine the reference applied to said comparator means in accordancewith said select signals. Said processor means is also arranged to beresponsive to signals provided by said null position switch means.

The apparatus preferably comprises a carriage to which each string ofthe plurality of strings is arranged to be attached, the carriage beingmovable longitudinally of the strings whereby movement of the carriageis arranged to vary the pitch of all of said strings. A tremolo arm maybe coupled to said carriage and arranged to move said carriage.

The present invention also extends to a musical instrument comprising atleas% one stretched string, and apparatus as defined above for varyingthe pitch of the string.

Where more than one string is provided, %he apparatus may be arranged tovary the pitches of one or more strings individually, and/or of one ormore of the strings collectively. For example, means to move theapparatus may be provided so as to vary the pitch of all the stringstogether.

In one embodiment, said apparatus is separate from said instrument, butis coupled thereto. Alternatively, the apparatus may be mounted onsupport means carried by instrument. The support means may comprise acarriage movable relative to the instrument in a direction substantiallylongitudinally of a said string.

There may be provided force applying means for applying a force to saidcarriage which acts substantially against the tension of the string orstrings. Said force applying means may comprise one or more springs. Thecarriage may comprise one or more pinions arranged for movement relativeto the instrument, for example along one or more racks. Preferably,means are provided for moving said carriage relative to the instrumentthereby to vary the pitch of the strings. Said means for moving maycomprise a tremolo arm coupled to said carriage.

In a preferred embodiment, said musical instrument is a guitar. Thedetecting means of said apparatus may comprise a plurality of sensorsmounted on the bridge of the guitar with which the strings are arrangedto come into contact. Preferably an individual sensor is provided foreach string of the plurality of strings.

Embodiments of the present invention are hereinafter described, by wayof example, with reference to accompanying drawings, in which:

FIG. 1 shows a plan view of part of the body of a guitar incorporating afirst embodiment of apparatus of the invention;

FIG. 2 shows a side elevational view of the apparatus of FIG. 1;

FIG. 3 shows a block diagram of electronic circuitry associated with theapparatus of FIGS. 1 and 2;

FIG. 4 shows a plan view of part of the body of guitar incorporating asecond embodiment of apparatus of the invention; and

FIG. 5 shows a side elevational view of the apparatus of FIG. 4.

FIG. 1 shows a plan view of apparatus 1 for automatically varying thepitch of the strings of a guitar. The apparatus 1 is received in arecess in the body 15 of a guitar to replace the conventional stringanchoring bar and the guitar bridge. Six strings 12 are attached at oneof their ends to the apparatus 1 and extend along the neck (not shown)of the guitar. The other end of each of the strings 12 is anchored tothe guitar neck 13 for example, by conventional tensioning pegs 11. Eachstring 12 is stretched or tensioned such that it produces a tone whenvibrated.

A conventional pick-up 16 is fitted to the guitar body 15 proximate thestrings 12. A tremolo arm 18 is provided on the guitar body 15, and isconnected to the apparatus 1.

FIG. 1 only shows a part of the guitar body 15 for clarity, and becausethe parts thereof which are not illustrated are preferably conventional.

It will be understood that the strings of a guitar are adjusted, forexample, by adjusting their tension and/or length to adjust the pitch ofthe tone they produce when vibrated. Commonly, one of the stretchedstrings is tuned by ear to a reference pitch or frequency and theremaining strings are then tuned by ear to have pitches atpredetermined, differing intervals from the reference.

As a tuned guitar is being played, one or more of the strings may becomeout of tune. However, if the player of the guitar is giving aperformance it is difficult to re-tune the instrument because of theneed for the player to listen to the pitches being produced, and alsobecause of the time needed, especially where a number of the stringsneed to be re-tuned. The apparatus 1 illustrated enables automatic,silent and quick re-tuning in these circumstances.

The apparatus 1 illustrated comprises six adjusting mechanisms 10 whichare arranged side-by-side. The one end of each string 12 is attached toa respective one of the adjusting mechanisms 10. Each said adjustingmechanism 10 is electronically actuable to adjust the tension of itsrespective string 12 to thereby alter the pitch of that string. The sixadjusting mechanisms 10 are located on one side of a guitar bridge 14remote from the neck of the guitar.

The adjusting mechanisms 10 are each substantially identical. A sideelevational view of one of the adjusting mechanisms 10 is shown in FIG.2. The adjusting mechanism 10 illustrated is supported on a carriage 42of the apparatus 1 and comprises an elongate tubular member 20 withinwhich the respective string 12 extends. The tubular member 20 acts toguide the string 12 to the top of the bridge 14. An anchoring point (notshown) for said one end of the string is provided within an enlarged endportion 24 of the tubular member 20.

With the exception of its two end portions, the outer surface of thetubular member 20 is screw-threaded. This screw-thread co-operates withthe screw-threaded inner surface of a central aperture (not shown) of agear-wheel 26. A pair of elongate, substantially parallel plates 28extend upwardly from the carriage 42 and provide support for thegear-wheels 26 of one or more of the adjusting mechanisms 10. As can beseen in FIG. 1, in the illustrated embodiment the plates 28 providesupport for the three gear-wheels 26 of three adjusting mechanisms,whilst the gear-wheels 26 of the three alternate adjusting mechanismsare supported by a second pair of substantially parallel, upstandingplates 28'. Furthermore, the plates 28, 28' are apertured (not shown)for the passage there through of the tubular members 20 such that theplates 28, 28' provide support for the tubular members 20. The plates28, 28' of each pair are located on opposite sides of each gear-wheel 26which is to be supported thereby. Each gear-wheel 26 is connected to thetwo plates of the respective pair by way of low-friction coupling means30 enabling rotation of the supported gear-wheel 26. For example, and asillustrated, said coupling means 30 may comprise a plurality of ballbearings held captive in the sides of the gear-wheel 26 and engaged in arespective annular groove (not shown) formed in the facing surface ofeach of said plates 28, 28'. Each such annular groove will surround anaperture in the plates 28, 28' through which the respective tubularmember 20 extends.

Each adjusting mechanism 10 comprises an electric drive motor 34 forrotating its tubular member 20. For example, the drive motor 34 may havea drive shaft (not shown) connected to a drive gear 32 engaged with thegear-wheel 26. In the embodiment illustrated, the diameter of the drivegear 32 is smaller than that of the gear-wheel 26. It will beappreciated that actuation of the drive motor 34 causes rotation of thegear-wheel 26 and hence, by way of the coupling means 30, causes thetubular member 20 to be moved longitudinally. The direction of rotationof the gear-wheel 26 determines whether the tubular member moves forwardor back, that is, to the left or to the right as seen in FIG. 2.

Further support for each tubular member 20 is provided by a third plate36 upstanding from said carriage 42. This plate 36 slidably receives anunthreaded front portion 21 of each tubular member 20 through arespective aperture (not shown) therein. In order to prevent rotation ofeach tubular member 20, the outer surface of its front portion 21 andthe corresponding aperture in the plate 36 are square in cross-section.Alternatively, flats may be provided on the front portion 21 of eachsaid tubular member.

A respective micro-switch 38, supported on the carriage 42, is providedproximate the rear end of each tubular member 20 and is arranged to beswitched by contact with the enlarged end portion 24 of that tubularmember 20. Each switch 38 is positioned such that when the respectivetubular member 20 is at a null position, it contacts the micro-switch 38and switches it into an off position. In addition, each adjustingmechanism is arranged such that the gear-wheel 26 thereof is at anintermediate position along the screw-threaded portion of the tubularmember 20. This ensures that the tubular member 20 can be moved bothforwardly and rearwardly relative to the null position. As it does so,the tubular member 20 causes the micro-switch 38 to be movedcorrespondingly forwardly or rearwardly take up a positive or negativeon position. The tubular member 20 would be positioned in its nullposition when a new string 12 is being attached thereto, for example,when the guitar is being restrung.

The bridge 14 of the apparatus 1 is carried by the carriage 42 andextends upwardly to space the strings 12 above the body 15 of theguitar. The bridge 14 is provided with six piezoelectric pick-ups orsensors 40 along the top thereof, each of which is arranged to becontacted by a respective string 12.

The carriage 42 which supports the six adjusting mechanisms 10 and thebridge 14 is retained within a recess 44 within the guitar body 15. Thecarriage 42 is movable within the recess 44 along a pair of racks 50(seen in better detail in FIG. 1) which extend longitudinally along thebase of the recess 44. Longitudinally spaced pinions 52, 54 and 56 arefitted to each side of the carriage. 42 and are arranged to run along arespective rack 50. Three coil springs 58 attach the rear end of thecarriage 42 to the rear end of the recess 44 and act to urge thecarriage 42 rearwardly.

The tension of the stretched strings 12 acts in opposition to the forceof the coil springs 58 and this causes the carriage 42 to adopt apredetermined position along the racks 50, and hence relative to theguitar body 15, and to maintain this position, for example, whilst theguitar is played. The bridge 14 is positioned on the carriage 42 sothat, when the carriage 42 is in its predetermined position, the bridge14 has the required mathematical correspondence with the position of thefrets on the finger board of the guitar neck.

The tremolo arm 18 is connected to one of the front pinions 56 of thecarriage 42 such that pivoting of the arm 18 rotates that pinion andthereby moves the carriage 42 along the racks 50. It will be apparentthat in so doing, the tension of all six strings 12 will be variedtogether whereby a tremolo sound of varying pitch is produced which issimilar to that provided by known tremolo arms. A locking device (notshown) may be provided to lock the carriage 42 in position, and therebyto lock the tremolo arm.

A removable cover plate 60 is provided for enclosing the apparatus 1 inthe recess 44. In the embodiment illustrated, a unit 62, which is formedof a key pad and a display, is supported by the cover plate 60.

The operation of the apparatus 1 is controlled by means of electroniccircuitry. In this respect, signals produced by the piezoelectricsensors 40 of the bridge 14 are used in controlling the operation of themotors 34 and thereby to vary the tension of the strings 12.

A block diagram of an electronic circuit which is associated with one ofthe strings 12 and its corresponding adjusting mechanism 10 is shown inFIG. 3. As can be seen, the piezoelectric sensor 40, which is contactedby the string 12, is connected to a band-pass filter 74 via an amplifier72. The piezoelectric sensor 40 is arranged to produce an output signalwhich depends upon the frequency of the vibration of the string 12, andhence upon the pitch of that string. The band-pass filter 74 removesunwanted components, such as harmonics, from the output signal. Thesignal output from the band-pass filter 74 will be substantiallyperiodic and representative of the pitch of the string.

The output of the band-pass filter 74 is connected to a pulse shaper 76arranged to modify the signal to produce an output in a form suitablefor driving a digital counter 78. The counter 78 is arranged to beactuated by the signal produced by the pulse shaper 76 so as to producean output count which is representative of the pitch of the string. Forexample, the signal output from the pulse shaper 76 may be fed to thecounting input of the counter 78 and arranged to enable the counter fora predetermined time period. Alternatively, the output from the pulseshaper 76 may be used to enable the counter 78 whilst a signal having apredetermined reference frequency is fed to the counting input. Theoutput count of the counter 78 thereby produced is applied to one inputof a digital comparator 84.

The key pad and display unit 62 is connected by way of a suitableinterface to a memory 80 which is connected to a selector buffer 82. Thememory 80 is arranged to store reference values which are representativeof various pitches, and preferably also stores standard values which arerepresentative of preselected reference pitches. Preferably, at leastsaid standard values are stored in non-volatile memory and preferably inread only memory. In an embodiment, the memory 80 is generally randomaccess memory (RAM), but a portion thereof is read only memory, such asROM or EPROM.

The selector buffer 82 is arranged, by instructions fed by way of theunit 62, to select from memory 80 an appropriate reference value, whichis representative of the pitch to which the associated string is to betuned. This reference value is fed to a second input of the digitalcomparator 84. The digital comparator 84 can then compare two inputs,that is, the output count from counter 78 which is representative of theactual pitch, and the reference value, and produce an output voltage independence upon the comparison. The output of the comparator 84 is fedby way of an amplifier 86 to the drive motor 34.

The null-point micro-switch 38 is connected, by way of control circuitry(not shown), to the selector buffer 82. In addition, the pick-up 16 isconnected to a substantially conventional output 90 by way of a mutecircuit 88. The mute circuit 88 is also connected to the key pad anddisplay unit 62.

During tuning, the string 12 is made to vibrate so that thepiezoelectric sensor produces a voltage signal across its output. Theelectrical output signal from the piezoelectric sensor 40, which willcontain components of various frequencies, one of which isrepresentative of the pitch, is amplified by the amplifier 72. Thefiltered signal output from the band-pass filter 74 is fed to the pulseshaper 76 which generates an output in the form of periodic pulsessuitable for actuating the digital counter 78. It will be apparent thatthe frequency of the pulses will correspond to, or be representative of,the sound pitch.

The counter 78 is actuated to count in accordance with the frequency ofthe incoming pulses, and so produces an output count representative ofthe sound pitch. This count is then compared to the reference value,selected from the values stored in memory 80, by the digital comparator84. The comparator 84 produces an output which is dependent upon theresult of the comparison. If the count from the counter 78 is greaterthan the reference value, the output of the digital comparator 84 willbe positive, whilst if the count is lower than the reference value, theoutput of the comparator 84 will be negative. If the two outputssubstantially coincide, the digital comparator 84 produces no output,which is indicative of the string 12 being tuned to the pitchrepresented by the selected reference value.

If the output of the digital comparator 84 is positive, the drive motor34 is actuated to cause rotation of gear-wheel 26 in a direction to movethe tubular member 20 forwardly, that is, to the left as shown in FIG.2. This reduces the tension of the string 12 attached to the member 20,and also reduces the pitch of the stretched string. If the output of thecomparator 84 is negative, the drive motor 34 is actuated to rotate thegear-wheel 26 in the opposite direction so as to move the tubular member20 rearwardly. This increases the tension of the stretched string 12 andincreases its pitch. It will be appreciated that appropriate actuationof the drive motor 34 is continued until the actual pitch of the string12, represented by the output count of the counter 78, is at theselected frequency, represented by the selected reference value outputby the buffer 82.

In the embodiment illustrated each of the six adjusting mechanisms 10has a separate, associated electronic circuit so that each saidmechanism is independently actuatable. However, a single, common keypadand display unit 62 and a common memory 80 are preferably provided andconnected to all of the electronic circuits for all of adjustingmechanisms 10.

As shown, the key pad and display unit 62 are supported by the coverplate 60 of the recess 44 of the guitar body 15. Conveniently, theelectronic circuits for the adjusting mechanisms 10 may also besupported by the cover plate 60 or otherwise by the guitar body 15 in,or adjacent to, the recess 44. For example, a printed circuit board (notshown) carrying the electronic circuits may be supported by the coverplate 60 or within the carriage 42.

The key pad of the unit 62 is provided with a number of control keys(not shown). For example, these control keys may comprise a master key;six individual string keys; input keys, associated with a mode key, toset reference values into memory; a tuning key; a reference pitch key,for use in tuning a string to a standard reference pitch; a null key,for setting an adjusting mechanism 10 to its null position; and a mutekey. Control logic or software enables program routines to be enabled byactuation of the keys. In this respect, appropriate processor means (notshown) are provided, for example, in said unit 62 and/or associated withthe memory 80.

The display of the unit 62 comprises a liquid crystal display associatedwith the key pad, and a second display. The second display is providedwith six sets of light emitting diodes (LEDs) for indicating the stateof tubing of each of the strings. Each set of LEDs is associated withone string and comprises a first LED arranged to be illuminated when thepitch is below a selected frequency, a second LED arranged to beilluminated when the pitch is above a selected frequency, and a thirdLED which is arranged to be illuminated when the string has a pitchtuned to a selected frequency. For the convenience of the guitar player,each set of LEDs is preferably positioned proximate its correspondingstring 12.

The master key (not shown) on the key pad enables actuation of all sixof the adjusting mechanisms 10 simultaneously. Thus, for example, allsix strings may be tuned to an individually selected pitch by actuatingthe tuning key together with the master key. This starts a tuningroutine for all of the strings in which each of the six digital counters78 is caused to count incoming pulses and to apply the output count tothe comparator 84, and the associated selector buffer 82 applies aselected reference value to the comparator 84 to produce an appropriatecomparator output. As described previously, the output of the comparatoris used to actuate the drive motor of the corresponding adjustingmechanism.

If it is required to tune only one of the strings 12, the string key forthat string is activated together with the tuning key. This causes atuning routine for the single selected string to be run. Similarly,tuning routines for selected ones of the strings are selected byactivating the tuning key together with the corresponding string keys.Thus, any one or any combination of the six strings 12 can be tunedindividually or together to pitches selected for the strings concerned.

The input keys are used to enable reference values representative ofrequired pitches for each of the strings to be input into memory 80. Towrite reference values into memory 80, the mode key is activated toselect "programming mode". The input keys, typically representing thenumbers 0 to 9, are then activated to cause a number representative ofthe required pitch to be displayed on the LCD display. When set, thereference number of the selected pitch is written into memory 80 byactivating either the master key, or one or more of the individualstring keys. Activation of the master key stores the selected referencevalue in memory locations of the memory 80 associated with all six ofthe strings so that all of the strings can be tuned to the selectedpitch. On the other hand, activation of an individual string key willstore the selected reference value in a memory location of the memory 80associated with the associated single string, so that that string can betuned to the selected pitch.

Generally, the guitar player will find it easier to set values for therequired string pitches which are presented in musical notation. Thus,the input keys may be arranged to represent, or to successively display,the tones A-G and each octave. A program routine, for example, utilisinga look-up table in memory, is then arranged to produce a reference valuefor storage in memory which corresponds to a selected tone.

During a tuning routine, the reference values are accessed from thememory 80 by activating the tuning key and, as required, the master keyor one or more individual string keys. As described above, when themaster key is activated, each string is tuned to the pitch representedby the reference value stored for that string. However, when individualstrings are tuned, this can be to the pre-selected associated pitch, orto any of the other pitches represented by the stored reference values.The strings can thus be tuned to non-standard pitches.

The reference pitch key is used in combination with the tuning key andeither the master key or one or more of the individual string keys, totune one or more of the strings to a pre-programmed standard referencepitch. When these keys are activated, the selector buffer 82 is arrangedto access the read only memory in which standard values corresponding topre-selected reference pitches are stored. The accessed standard valuesare then used in the actuated tuning routine in the manner describedabove.

Normally it is arranged that the output 90 is disabled during tuningoperations. However, activation of the mute key is arranged to maintainthe output enabled during tuning operations. The player is thus able tohear the changes in pitch of the or each string as tensions are changed.

When a new string 12 is to be fitted to the guitar, the correspondingadjustment mechanism 10 is set null position by activating the null keyand the associated individual string key. It will be recalled thatmovement of the adjustment mechanism 10 causes the micro-switch 38 toassume a positive or a negative on position. Activation of the null keycauses the selector buffer 82 to look at the condition of themicro-switch 38 and to cause an appropriate output value to be fed tothe comparator 84 generate a positive or negative output to actuate thedrive motor 34. When the null position of the tubular member 20, andhence of the adjustment mechanism 10, is reached, the micro-switch 38 isswitched to its off position and no further movement of the adjustingmechanism is caused. The string can then be fed through the tubularmember 20. The end of the string is knotted or has a suitable stop fixedto it, and this stop or knotted end is anchored to the anchoring pointwithin the enlarged end portion 24. The other end of the string 12 isfed onto its respective tensioning peg at the stringing head (not shown)of the guitar neck.

The newly strung string is brought coarsely into tune manually byactivation of the tensioning peg, and then adjusting mechanism 10 isactuated, by activation of the tuning key and the correspondingindividual string key or the master key, to tune the string to the pitchrepresented by the stored reference value.

Positioning the adjusting mechanism 10 at its null point prior to tuningthe newly strung string ensures the adjusting mechanism 10 can be movedin either direction during tuning so as to increase or decrease thetension of the string.

It will be appreciated that the apparatus enables newly strung guitarstrings to be quickly and easily tuned to the selected pitch.

One or more strings can be re-tuned by activating the tuning key and themaster key or the appropriate individual string keys. If one or more ofthe strings have been tuned to non-standard pitches, activation ofappropriate keys will enable the apparatus to re-tune these strings tothe standard reference pitches. As will be appreciated, tuning andre-tuning operations undertaken by the apparatus are performed veryrapidly, for example, in a few seconds.

The software determining the program routines described above is notfurther described herein as production will be within the competence ofanyone skilled in the art.

In the embodiment illustrated in FIGS. 1 to 3, the pitch of a string 12is adjusted by moving the associated tubular member 20 forwardly orrearwardly by way of a respective gear wheel 26. It will be appreciatedthat the drive motor 34 has to develop sufficient power to cause thismovement, and there can be difficulties in providing a drive motor 34which is small enough and yet sufficiently powerful.

FIGS. 4 and 5 show an alternative embodiment in which a less powerfuldrive motor can be used. In this respect, in the embodiment of FIGS. 4and 5, each string 12 is held at a tensioned, null position, by a springforce. This means that the drive motor 34 needs only to be able to poweradjustment of the tension of the corresponding string 12, rather thanhaving to supply all of the tension of the string 12 as in the previousembodiment.

In FIGS. 4 and 5, parts and features which are the same or similar toparts and features of the embodiment of FIGS. 1 and 2 have been giventhe same reference numerals.

As previously, the apparatus 1 shown in FIGS. 4 and 5 comprises sixadjusting mechanisms 10 which are arranged side by side, and the one endof each string 12 is attached to a respective one of the adjustingmechanisms 10. The six adjusting mechanisms 10 are located on one sideof a guitar bridge 114 remote from the neck of the guitar. In thisembodiment, the brige is formed by individual bridge pieces 114 each inthe form of a roller.

As before, the six adjusting mechanisms 10 are each substantiallyidentical, and a side elevational view of one of them is shown in FIG.5. The adjusting mechanism 10 illustrated is supported on the carriage42 and comprises an elongate tubular member 20 within which therespective string 12 extends. The tubular member 20 acts to guide thestring 12 to the top of the bridge 114. An anchoring point (not shown)for said one end of the string is provided within the tubular member 20.

The outer surface of the tubular member 20 is screw-threaded. Thisscrew-thread co-operates with the threaded interior of a spur gear 26supported between a pair of substantially parallel mounting plates 28.In the embodiment of FIG. 4, four spaced plates 28 provide support forthe six spur gears 26. As before, the plates 28 are apertured (notshown) so that the tubular members 20 can extend therethrough and beprovided with support. Each spur gear 26 is connected to the two plates28 of the respective pair by way of low-friction coupling means 130enabling rotation of the supported gear 26. For example, and asillustrated, said coupling means 130 may comprise a respective thrustbearing 130 interposed between one side of the gear 26 and a facingsurface of the adjacent plate 28.

The drive motor 34 of each adjusting mechanism 10 is, in thisembodiment, provided with a worm drive 132 engaging with the gear 26 forrotating its tubular member 20. Although each d.c. drive motor 34 isarranged to cause rotation of the gear 26, and hence to move the Tubularmember 20 longitudinally, in the embodiment of FIGS. 4 and 5 biassingmeans are arranged to support the tension in the strings 12 and toeffectively provide a coarse adjustment for this tension. In theillustrated embodiment, the biassing means associated with each string12 comprises a coil spring 124 having one end fixed to the rear end ofthe tubular member 20 and its other end fixed to a spring adjuster andlock nut 126. As the adjuster 126 is adjusted to compress the spring124, increasing tension is applied to the string 12 against the springforce of the coil spring 124. Thus, in the null position, the tension inthe string 12 is balanced by the force of the coil spring 124. Thismeans that a relatively small force from the drive motor 34 will be ableto provide a fine adjustment of the string tension. It is also meansthat the null position is set by the adjusted condition of the coilspring 124 and that a micro-switch or other means to establish the nullposition is not required.

In the embodiment of FIGS. 4 and 5, the sensors 40 for the individualstrings 12 are carried by a bridge support 140 which also supports thebridge pieces 114.

As previously, the carriage 42 is movable along a pair of longitudinalracks 50, but in this embodiment, this is by way of a pair oflongitudinally spaced pinions 52 and 56. The carriage 42 is urgedrearwardly by way of the three coil springs 58 attached to the rear endof the carriage 42. It is the tension of the stretched strings 12 actingin opposition to the force of the coil springs 58 which causes thecarriage 42 to adopt a predetermined position relative to the guitarbody 15. The tremolo arm 18 is connected to one of the front pinions 56of the carriage 42 such that pivoting of the arm 18 rotates that pinionand thereby moves the carriage 42 along the racks 50.

The operation of the apparatus 1 of the embodiment of FIGS. 4 and 5 issubstantially as described above with reference to FIGS. 1 and 2.However, in the electronic circuit as shown in FIG. 3 the micro-switch38 can be omitted.

In the embodiments described above, the electronic circuits forcontrolling the adjusting mechanisms, the display and monitoring meansassociated therewith, and the user input interface, in the form of thekey pad, are all positioned on the guitar body. However, it will beappreciated that any one of these integers may be arranged at a remotelocation and suitably coupled or connected to the guitar. In particular,players may find it convenient to be provided with an input interfacearranged in the form of one or more foot pads or pedals.

The tremolo arm 18 is connected to the apparatus 1 such that pivoting ofthe arm causes a sound of varying pitch. If required, this effect canalso be caused by actuation of the adjusting mechanisms by way of theelectronic circuits. For example a tremolo program routine can bearranged to apply differing reference values to each of the comparators84 whereby a continuous tuning operation is carried out whilst theguitar is played. As previously, movement of the adjusting mechanismswill cause the tensions of the strings 12 to vary in accordance with thechange in reference values.

In the embodiments described, the pitch of each string is varied byadjusting its tension. However, it will be appreciated that additionallyand/or alternatively the adjusting mechanisms may vary the effectivelength of the strings. Furthermore, whilst the invention has beendescribed specifically with reference to guitars, apparatus of theinvention may be used to vary the tuning of any instrument comprisingstretched strings.

Other modifications and alterations to the above described embodimentmay be made within the scope of the invention.

I claim:
 1. Apparatus arranged to automatically vary the pitch of astring, said apparatus comprising:a string having first and secondspaced ends; an adjusting mechanism coupled to said first end of saidstring; and anchoring means for anchoring said second end of saidstring: said string being stretched and tensioned between said adjustingmechanism and said anchoring means; said adjusting mechanism comprisinga movable adjustment member to which said first end of the string isanchored; a drive motor; means for coupling said drive motor to saidadjustment member such that rotation of said drive motor moves saidadjustment member and thereby adjusts the tension of the string;detecting means arranged to produce a signal representative of the pitchproduced by vibration of the string; comparing means arranged to comparesaid representative signal with a predetermined reference and to producean output dependent upon said comparison; and means for applying theoutput of said comparing means to said drive motor to rotate the drivemotor thereby adjusting the tension applied to said string in responseto said output of said comparing means; wherein said adjusting mechanismfurther comprises resilient biasing means coupled to said movableadjustment member to bias said adjustment member in a direction opposingthe tension of the; wherein said detecting means comprises pulsegenerating means for generating periodic pulses having a frequencyrepresentative of the pitch of the vibration of the string, and acounter receiving said periodic pulses and producing an output countrepresentative of said pitch; and wherein said adjustment membercomprises a screw-threaded member attached to said end of said string,and said means for coupling said drive motor to said adjustment membercomprises one or more gears.
 2. Apparatus according to claim 1, whereinsaid gear is arranged to be rotated by said drive motor and cooperateswith the screw-thread of said adjustment member whereby rotation of saidgear causes movement of said member longitudinally of the stringattached thereto.
 3. Apparatus according to claim 2, wherein saidadjustment member comprises a tubular member within which the stringextends, said screw-thread being provided externally of said tubularmember and arranged for engagement with said gear.
 4. Apparatusaccording to claim 1, wherein said comparing means is a digitalcomparator, and further comprising a memory arranged to store aplurality of reference values, and selector means for selecting one ofthe stored values for use as the reference by said comparator. 5.Apparatus according to claim 4, wherein interface means are provided andare arranged to enable the input and/or variation of the values storedin said memory.
 6. Apparatus according to claim 4, further comprisingindicator means responsive to the output of said comparator. 7.Apparatus according to claim 6, wherein said indicator means comprisevisual display means.
 8. Apparatus according to claim 1, wherein saiddetecting means comprises a vibration sensor arranged proximate to, orin contact with, said string.
 9. Apparatus arranged to automaticallyvary the pitch of a plurality of strings, said apparatus comprising:aplurality of strings, each said string having first and second spacedends; a plurality of adjusting mechanisms, each said adjusting mechanismbeing coupled to the first end of a respective one of said strings;anchoring means anchoring the second ends of the strings; each saidstring being stretched and tensioned between a respective one of saidadjusting mechanisms and said anchoring means; each said adjustingmechanism comprising a moveable adjustment member to which said firstend of said respective one of said strings is anchored; a drive motor;and means for coupling said drive motor to one of said adjustmentmembers such that rotation of said drive motor moves said one of saidadjustment members and thereby adjusts the tension of the respective oneof the strings; wherein each said adjusting mechanism further comprisesresilient biasing means coupled to each said movable adjustment memberto bias each said adjustment member in a direction opposing the tensionof the respective one of the strings, and each said adjustment membercomprises a screw-threaded tubular member within which each said stringextends, one of said screw-threaded tubular members being coupled tosaid drive motor by said coupling means.
 10. Apparatus according toclaim 9, wherein said coupling means comprises a gears arranged to berotated by said drive motor and cooperating with the screw-thread ofsaid one of said tubular members whereby rotation of said gear by saiddrive motor causes movement of said one of said tubular memberslongitudinally of the respective one of said strings attached thereto.11. Apparatus according to claim 9, further comprising detecting meansarranged to produce a signal representative of the pitch produced byvibration of one of said plurality of strings, and comparing meansarranged to compare said representative signal with a selectedreference.
 12. Apparatus arranged to automatically vary the pitch of aplurality of strings, said apparatus comprising:a plurality of strings,each said string having first and second spaced ends; a plurality ofadjusting mechanisms, each said adjusting mechanism being coupled to thefirst end of a respective one of said strings; anchoring means anchoringthe second ends of the strings; each said string being stretched andtensioned between a respective one of said adjusting mechanisms and saidanchoring means; each said adjusting mechanism comprising a moveableadjustment member to which said first end of said respective one of saidstrings is anchored; a drive motor; and means for coupling said drivemotor to one of said adjustment members such that rotation of said drivemotor moves said one of said adjustment members and thereby adjusts thetension of the respective one of the strings; wherein each saidadjusting mechanism further comprises first resilient biasing meanscoupled to each said movable adjustment member to bias each saidadjustment member in a direction opposing the tension of the respectiveone of the strings; and wherein said apparatus further comprises amovable carriage on which each said adjusting mechanism is supported,second resilient biasing means for biasing said carriage to an initialposition; and a tremolo arm coupled to said carriage to move saidcarriage against the action of said second biasing means.
 13. Apparatusaccording to claim 12, wherein said carriage is movable longitudinallyof said strings whereby movement of the carriage is arranged to vary thepitch of all of said strings.
 14. Apparatus according to claim 12wherein each said adjustment member comprises a screw-threaded tubularmember within which the respective one of said strings extends, one ofsaid screw-threaded tubular members being coupled to the drive motor bysaid coupling means.
 15. Apparatus according to claim 12, furthercomprising detecting means arranged to produce a signal representativeof the pitch produced by vibration of one of said plurality of strings,and comparing means arranged to compare said representative signal witha selected reference.
 16. Apparatus according to claim 15, furthercomprising storage means for storing a plurality of reference values,and selector means for selecting one of the stored values for use as thereference by said comparing means.
 17. Apparatus according to claim 16,wherein interface means are provided and are arranged to enable theinput and/or variation of the values stored in the storage means. 18.Apparatus according to claim 16, further comprising visual display meansarranged to be responsive to the output of said comparing means. 19.Apparatus according to claim 16, wherein said detecting means arrangedto produce a signal representative of pitch is a vibration sensorarranged proximate to, or in contact with, each said string.